1. Field of the Invention
The invention relates to a DC power supply using a fuel cell.
2. Description of Related Art
Fuel cells have been gaining much attention in recent years as a power supply with a high operation efficiency and environmental characteristics. A fuel cell generates electricity through an electrochemical reaction of hydrogen and oxygen and outputs electric power as required by controlling an amount of a fuel gas to be supplied. In some cases, however, the response of the electric power output is lowered due to the delay in supply of the fuel gas. In order to avoid the aforementioned problem, a technique in which a fuel cell and a battery are connected in parallel to constitute a power supply system has been proposed. For example, in Japanese Patent Laid-Open Publication No. 2000-12059, the output voltage of the fuel cell is converted by a DC-DC converter to allow usage of a battery and a fuel cell in combination. In the aforementioned structure, however, the electric power output efficiency is desired to be further improved.